JP6158377B2 - Solid polymer electrolyte fuel cell - Google Patents

Description

  The present invention relates to a membrane electrode assembly and a solid polymer electrolyte fuel cell.

A fuel cell is one that converts the chemical energy of fuel directly into electrical energy by electrochemically oxidizing hydrogen, methanol, etc. in the battery, and is attracting attention as a clean electrical energy supply source. ing. In particular, solid polymer electrolyte fuel cells are expected to be used as alternative power sources for automobiles, home cogeneration systems, portable generators, and the like because they operate at a lower temperature than other fuel cells.
Such a solid polymer electrolyte fuel cell includes at least a membrane electrode assembly in which a gas diffusion electrode in which an electrode catalyst layer and a gas diffusion layer are laminated is bonded to both surfaces of a proton exchange membrane. The proton exchange membrane here is a material having a strong acidic group such as a sulfonic acid group and a carboxylic acid group in the polymer chain and a property of selectively transmitting protons. As such a proton exchange membrane, a perfluoro proton exchange membrane represented by Nafion (registered trademark, manufactured by DuPont) having high chemical stability is preferably used.

A solid polymer electrolyte fuel cell includes a membrane electrode assembly in which an electrode catalyst layer, that is, an anode catalyst layer including an anode catalyst and a cathode catalyst layer including a cathode catalyst are bonded to both surfaces of a proton exchange membrane which is a polymer electrolyte membrane. (Hereinafter sometimes abbreviated as “MEA”). Moreover, what joined a pair of gas diffusion layers so that it might oppose further on the outer side of an electrode catalyst layer may be called MEA.

  During operation of the solid polymer electrolyte fuel cell, fuel (for example, hydrogen) is supplied to the gas diffusion electrode on the anode side, and oxidant (for example, oxygen or air) is supplied to the gas diffusion electrode on the cathode side. By connecting with an external circuit, the operation of the fuel cell is realized. Specifically, when hydrogen is used as fuel, hydrogen is oxidized on the anode catalyst to generate protons. After passing through the proton conductive polymer in the anode catalyst layer, the protons move in the proton exchange membrane and reach the cathode catalyst through the proton conductive polymer in the cathode catalyst layer. On the other hand, electrons generated simultaneously with protons by oxidation of hydrogen reach the cathode side gas diffusion electrode through an external circuit. On the cathode catalyst, the proton and oxygen in the oxidant react to generate water. At this time, electric energy is extracted.

  Patent Document 1 discloses an electrode catalyst having a perfluorocarbon sulfonic acid resin having an equivalent weight (hereinafter also referred to as “EW”) of 555 to 715 and including a repeating unit having two specific functional groups in the side chain. Techniques using layers are disclosed. Patent Document 2 discloses a technique in which a proton conductive perfluorocarbon sulfonic acid resin having EW250 to EW680 is used as an electrode catalyst layer together with catalyst particles.

JP 2008-186784 A JP 2010-225585 A

  A solid polymer electrolyte fuel cell is usually operated under high humidification conditions in order to obtain high output characteristics. At present, it is desired that the anode be operated under a lower humidification condition than the current situation, and the cathode should be operated under a non-humidification condition.

  A fuel cell equipped with a membrane electrode assembly using a conventional perfluorocarbon sulfonic acid resin membrane having a EW of about 1100 as a polymer electrolyte membrane, for example, Nafion (registered trademark, manufactured by DuPont), is particularly suitable under low humidification conditions. The actual situation is that the fuel cell cannot be operated under the condition of no humidification of the cathode. In addition, the electrode catalyst layers disclosed in Patent Document 1 and Patent Document 2 still have room for improvement in terms of output characteristics under cathode non-humidified conditions.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a membrane electrode assembly having high output even under a non-humidified condition of a cathode, and a solid polymer electrolyte fuel cell including the membrane electrode assembly. To do.

  As a result of intensive studies to achieve the above object, the present inventors have achieved the above object by having a specific relationship between the cathode catalyst layer and the anode catalyst layer provided in the membrane electrode assembly. As a result, the present invention was completed.

That is, the present invention is as follows.
(1) a polymer electrolyte membrane, sandwich the polymer electrolyte membrane from both sides, the anode catalyst layer, a cathode catalyst layer, comprising a membrane electrode assembly comprising a solid high operating the cathode electrode without humidification under conditions In the molecular electrolyte fuel cell, in the membrane electrode assembly, the anode catalyst layer and the cathode catalyst layer are each composed of composite particles including conductive particles and electrode catalyst particles supported thereon, And the composite particles carry 1 to 99% by mass of the electrocatalyst particles with respect to 100% by mass of the composite particles, and the polymer electrolyte in the anode catalyst layer at 25 ° C. The water content in water is 20 to 36%, and the water content in water at 25 ° C. of the polymer electrolyte in the cathode catalyst layer is 2 of the polymer electrolyte in the anode catalyst layer. Wherein at ℃ greater than water water content, equivalent weight of the polymer electrolyte in the cathode catalyst layer, 455-800 der is, the polymer electrolyte in the cathode catalyst layer is a perfluorocarbon sulfonic acid resin, The perfluorocarbon sulfonic acid resin has the following general formula (1):
_{- (CF 2 -CFZ) - (} 1)
(In formula, Z shows a hydrogen atom, a chlorine atom, a fluorine atom, or a C1-C3 perfluoroalkyl group.)
A repeating unit represented by the following general formula (2):
_{- (CF 2 -CF (-O- (} CF 2) m -SO 3 H)) - (2)
(In the formula, m is an integer of 1 to 12.)
A solid polymer electrolyte fuel cell, which is a copolymer having a repeating unit represented by:
(2) The solid polymer electrolyte fuel cell according to (1), wherein an equivalent weight of the polymer electrolyte in the cathode catalyst layer is 100 to 1000 smaller than an equivalent weight of the polymer electrolyte in the anode catalyst layer .

  According to the present invention, it is possible to provide a membrane electrode assembly having a high output even under a non-humidified condition of the cathode, and a solid polymer electrolyte fuel cell including the membrane electrode assembly.

  Hereinafter, the best mode for carrying out the present invention (hereinafter referred to as “the present embodiment”) will be described in detail. In addition, this invention is not limited to the following embodiment, It can implement by changing variously within the range of the summary.

  The membrane electrode assembly of the present embodiment includes a polymer electrolyte membrane, and an anode catalyst layer and a cathode catalyst layer that sandwich the polymer electrolyte membrane from both sides. The anode catalyst layer is an electrode catalyst layer for a fuel cell as an anode (hereinafter also simply referred to as “electrode catalyst layer”), and the cathode catalyst layer is an electrode catalyst layer as a cathode. Each electrode catalyst layer includes a composite particle including conductive particles and electrode catalyst particles supported thereon, and a polymer electrolyte.

  First, the polymer electrolyte will be described. As the polymer electrolyte used in the present embodiment, for example, a perfluorocarbon polymer compound having an ion exchange group, or a compound obtained by introducing an ion exchange group into a hydrocarbon polymer compound having an aromatic ring in the molecule is preferable. Examples of the hydrocarbon polymer compound having an aromatic ring in the molecule include polyphenylene sulfide, polyphenylene ether, polysulfone, polyether sulfone, polyether ether sulfone, polyether ketone, polyether ether ketone, polythioether ether sulfone, Polythioether ketone, polythioether ether ketone, polybenzimidazole, polybenzoxazole, polyoxadiazole, polybenzoxazinone, polyxylylene, polyphenylene, polythiophene, polypyrrole, polyaniline, polyacene, polycyanogen, polynaphthyridine, polyphenylene sulfide sulfone, polyphenylene sulfone , Polyimide, polyetherimide, polyesterimide, polyamideimide, polyester Arylate, aromatic polyamide, polystyrene, polyester and polycarbonate. A polymer electrolyte is used individually by 1 type or in combination of 2 or more types.

  Among these, the hydrocarbon polymer compound having an aromatic ring in the molecule includes polyphenylene sulfide, polyphenylene ether, polysulfone, polyether sulfone, polyether ether sulfone from the viewpoint of heat resistance, oxidation resistance, and hydrolysis resistance. , Polyetherketone, polyetheretherketone, polythioetherethersulfone, polythioetherketone, polythioetheretherketone, polybenzimidazole, polybenzoxazole, polyoxadiazole, polybenzoxazinone, polyxylylene, polyphenylene, polythiophene, polypyrrole, Polyaniline, polyacene, polycyanogen, polynaphthyridine, polyphenylene sulfide sulfone, polyphenylene sulfone, polyimide and polyether Soil is preferred. Examples of the ion exchange group introduced into the aromatic ring of the hydrocarbon polymer compound having an aromatic ring in the molecule include a sulfonic acid group, a sulfonimide group, a sulfonamide group, a carboxylic acid group, and a phosphoric acid group. And is preferably a sulfonic acid group.

  The polymer electrolyte used in the present embodiment is preferably a perfluorocarbon polymer compound having an ion exchange group from the viewpoint of chemical stability. Examples of the perfluorocarbon polymer compound having an ion exchange group include perfluorocarbon sulfonic acid resin, perfluorocarbon carboxylic acid resin, perfluorocarbon sulfonimide resin, perfluorocarbon sulfonamide resin, perfluorocarbon phosphoric acid resin, or these resins. Examples include amine salts and metal salts. Among these, perfluorocarbon sulfonic acid resin is particularly preferable.

  Although it does not specifically limit as a perfluorocarbon sulfonic acid resin in this embodiment, Copolymerization of the fluorinated vinyl ether compound represented by the following general formula (2A) and the fluorinated olefin monomer represented by the following general formula (1A) What is obtained by hydrolyzing a perfluorocarbon sulfonic acid resin precursor composed of a coalescence is preferable.

_{CF 2 = CF-O- (CF} 2 CFXO) n - (CF 2) m -W (2A)
Here, in formula (2A), X represents a fluorine atom or a C1-C3 perfluoroalkyl group, n is an integer of 0-5, and m is an integer of 0-12. However, n and m are not 0 at the same time. W is a functional group that can be converted to SO ₃ H by hydrolysis.
CF ₂ = CFZ (1A)
Here, in the formula (1A), Z represents a hydrogen atom, a chlorine atom, a fluorine atom, or a perfluoroalkyl group having 1 to 3 carbon atoms.

As W which is a functional group that can be converted to SO ₃ H by hydrolysis in the above formula (2A), SO ₂ F, SO ₂ Cl, or SO ₂ Br is preferable. In addition, in the above formulas (2A) and (1A), a perfluorocarbon sulfonic acid resin precursor in which X is CF ₃ , W is SO ₂ F, and Z is a fluorine atom is preferable, among which n is 0 and m is A viewpoint in which a solution with a high resin concentration can be obtained when 0 and 6 are integers (where n and m are not 0 simultaneously), X is CF ₃ , W is SO ₂ F, and Z is a fluorine atom. To more preferable.

  The perfluorocarbon sulfonic acid resin precursor can be synthesized by known means. For example, using a polymerization solvent such as fluorine-containing hydrocarbon, filling and dissolving the above-mentioned vinyl fluoride compound and fluorinated olefin gas and reacting them (solution polymerization), using a solvent such as fluorine-containing hydrocarbon Without polymerizing the vinyl fluoride compound itself as a polymerization solvent (bulk polymerization), using a surfactant aqueous solution as a medium, filling a vinyl fluoride compound and a fluorinated olefin gas, and reacting to polymerize (emulsification) Polymerization), a method in which an aqueous solution of a co-emulsifier such as a surfactant and alcohol is filled and emulsified with a vinyl fluoride compound and a fluorinated olefin gas, and then reacted (miniemulsion polymerization, microemulsion polymerization) and suspension. A method (suspension polymerization) in which a vinyl fluoride compound and a fluorinated olefin gas are charged and suspended in an aqueous solution of a stabilizer to cause polymerization (suspension polymerization). . In this embodiment, those synthesized by any polymerization method can be used.

The perfluorocarbon sulfonic acid resin has the following formula (1):
_{- (CF 2 -CFZ) - (} 1)
A repeating unit represented by the following general formula (2B):
_{- (CF 2 -CF (-O- (} CF 2 CFXO) n - (CF 2) m -SO 3 H)) - (2B)
A copolymer having a repeating unit represented by Here, in formula (1), Z is synonymous with that in formula (1A) above, in formula (2B), X is a fluorine atom or CF ₃ , n is an integer of 0 to 5, m Is an integer from 0 to 12. However, n and m are not 0 at the same time. When the perfluorocarbon sulfonic acid resin is a copolymer having the above structure, the membrane / electrode assembly tends to have high performance and resistance to hydrogen peroxide radicals generated during fuel cell operation.
Further, the perfluorocarbon sulfonic acid resin in the cathode catalyst layer includes a repeating unit represented by the above general formula (1) and the following general formula (2):
_{- (CF 2 -CF (-O- (} CF 2) m -SO 3 H)) - (2)
A copolymer having a repeating unit represented by Here, m is an integer of 1-12 in a formula. If the perfluorocarbon sulfonic acid resin is a copolymer having the above structure, the moisture content tends to be high and the proton conductivity tends to be improved.

  Further, in the general formula (2), it is more preferable that m is an integer of 1 to 6 from the viewpoint of power generation performance of the fuel cell.

In addition, in order to improve the durability of the perfluorocarbon sulfonic acid resin, the unstable terminal group of the precursor of the perfluorocarbon sulfonic acid resin may be stabilized. Examples of the unstable terminal group of the precursor include a carboxylic acid group (—COOH), a carboxylate group (—COOM; M is a metal atom forming a salt), a carboxylic acid ester group (—COOR; R is 1 Valent organic group), carbonate group (—OCOOR; R is a monovalent organic group), alkyl group, and methylol group (—CH ₂ OH). The unstable terminal group varies depending on the polymerization method, the type of initiator, chain transfer agent, polymerization terminator, etc. used in the polymerization method. For example, when emulsion polymerization is selected as the polymerization method and no chain transfer agent is used, most of the unstable end groups are carboxylic acid groups. The method for stabilizing the unstable terminal group of the precursor is not particularly limited. For example, the precursor is treated with a fluorinating agent to convert the unstable terminal group to —CF _3. Examples of the stabilization method include a method in which the precursor is heated and decarboxylated to convert the unstable end group to —CF ₂ H to be stabilized.

  In one example of the membrane electrode assembly in the present embodiment, the water content in water at 25 ° C. of the polymer electrolyte in the cathode catalyst layer is larger than the water content in water at 25 ° C. of the polymer electrolyte in the anode catalyst layer. The water content of the polymer electrolyte in water is determined by placing the polymer electrolyte in water at 25 ° C. for 1 hour, removing the water from the water and wiping off the water droplets on the surface (water content), and further at 160 ° C. The mass after drying (dry mass) is measured, and is expressed as the mass increase rate of the moisture content relative to the dry mass. In general, the water content in water is high when the equivalent weight (hereinafter also referred to as “EW”) is small, and low when the equivalent weight is large. Here, “equivalent weight” means the dry mass in grams of the polymer electrolyte per equivalent of proton exchange groups.

  As is apparent from the above, the water content of the polymer electrolyte in water at 25 ° C. can be adjusted by, for example, the equivalent weight. More specifically, the water content of the polymer electrolyte in water can be increased by reducing the equivalent weight.

  In addition, the polymer electrolyte in the present embodiment may be provided with water content by containing water-absorbing fine particles and / or fibrous silica. Furthermore, as a method of uniformly dispersing the amorphous water-absorbing material in the polymer electrolyte, a method of containing a water-absorbing metal oxide using a sol-gel reaction may be used.

  In the present embodiment, the water content in water at 25 ° C. of the polymer electrolyte in the anode catalyst layer is not particularly limited, but is preferably 10 to 200%, more preferably 10 to 100%, and still more preferably 20. ~ 100%. On the other hand, the water content in water at 25 ° C. of the polymer electrolyte in the cathode catalyst layer is not particularly limited, but is preferably 20 to 500%, more preferably 20 to 400%, and still more preferably 50 to 400%. is there.

  In the present embodiment, the difference in the water content in water at 25 ° C. between the polymer electrolyte in the cathode catalyst layer and the polymer electrolyte in the anode catalyst layer is the water content in water at 25 ° C. of the polymer electrolyte in the cathode catalyst layer. However, it is preferably 1.5 to 50 times greater than the water content of the polymer electrolyte in the anode catalyst layer at 25 ° C., more preferably 1.5 to 40 times greater, and even more preferably 2 to 20 times greater. . By setting the water content in water at 25 ° C. within the above range and allowing the composite particles described below to coexist, higher output can be realized during fuel cell operation without cathode humidification.

  In another example of the membrane electrode assembly in the present embodiment, the equivalent weight of the polymer electrolyte in the cathode catalyst layer is smaller than the equivalent weight of the polymer electrolyte in the anode catalyst layer. In this Embodiment, it is although it does not specifically limit as an equivalent weight of the polymer electrolyte in an anode catalyst layer, It is preferable that it is 350-2000, More preferably, it is 400-1500, More preferably, it is 500-1000. . On the other hand, the equivalent weight of the polymer electrolyte in the cathode catalyst layer is not particularly limited, but is preferably 250 to 1000, more preferably 300 to 900, and still more preferably 400 to 800. Since polymer electrolytes having low EW tend to have high proton conductivity, it is desirable to use them as polymer electrolytes in the cathode catalyst layer. When the EW is 250 or more, the heat-resistant water solubility tends to be sufficient, and when the EW is 1000 or less, a decrease in proton conductivity can be suppressed and sufficient protons can be easily supplied to the cathode. It is in. The equivalent weight of the polymer electrolyte can be measured by salt-substituting the polymer electrolyte and back titrating the solution with an alkaline solution.

  In the case of a perfluorocarbon sulfonic acid resin, the equivalent weight of the polymer electrolyte is, for example, a fluorinated vinyl ether compound (for example, one represented by the general formula (2A)) and a fluorinated olefin monomer (for example, the general formula (1A)). The polymerization ratio can be adjusted by changing the polymerization ratio. More specifically, the equivalent weight of the polymer electrolyte can be reduced by increasing the polymerization ratio of the fluorinated vinyl ether compound.

  The difference in equivalent weight between the polymer electrolyte in the anode catalyst layer and the polymer electrolyte in the cathode catalyst layer is not particularly limited, but the equivalent weight of the polymer electrolyte in the cathode catalyst layer is the same as the polymer electrolyte in the anode catalyst layer. It is preferably 100 to 1000 smaller than the equivalent weight, more preferably 150 to 1000 smaller, and still more preferably 200 to 1000 smaller.

  The polymer electrolyte in the anode catalyst layer and the polymer electrolyte in the cathode catalyst layer may be the same electrolyte or different electrolytes. In the case where the polymer electrolytes are different from each other, at least one of them is preferably a perfluorocarbon sulfonic acid resin. Furthermore, even if their high electron electrolytes are the same or different from each other, it is preferable that both are perfluorocarbon sulfonic acid resins, both of which are described above as preferred perfluorocarbon sulfonic acid resins, for example, A copolymer having a repeating unit represented by the general formula (1) and a repeating unit represented by the general formula (2) is more preferable.

  Next, composite particles in which catalyst particles are supported on conductive particles contained in the electrode catalyst layer according to the present embodiment will be described.

  The material constituting the conductive particles is not particularly limited as long as it has conductivity, and examples thereof include carbon black such as furnace black, channel black, and acetylene black, activated carbon, graphite, and various metals. These are used singly or in combination of two or more.

  The average particle diameter of the conductive particles is preferably 10 angstroms to 10 μm, more preferably 50 angstroms to 1 μm, and further preferably 100 angstroms to 5000 angstroms. When the conductive particles have such an average particle diameter that is made into fine particles, an effect of increasing the surface area and efficiently dispersing and supporting the catalyst particles can be obtained. The average particle diameter of the conductive particles can be measured visually with a transmission electron microscope.

  In the anode catalyst layer, the catalyst particles easily generate protons by oxidizing a fuel such as hydrogen, and in the cathode catalyst layer, water is produced by reacting protons and electrons with an oxidant such as oxygen and air. It has the function to generate.

  The material constituting the catalyst particles is not particularly limited as long as it contributes to the above reaction, but platinum is particularly preferable because the catalytic activity for the above reaction tends to be high. Moreover, in order to reinforce the resistance of platinum to impurities such as CO, those obtained by adding a noble metal such as ruthenium to platinum or those obtained by alloying them are also preferable. A noble metal is used individually by 1 type or in combination of 2 or more types.

  The average particle diameter of the catalyst particles is preferably from 10 angstroms to 1000 angstroms, more preferably from 10 angstroms to 500 angstroms, and further preferably from 15 angstroms to 100 angstroms. When the catalyst particles have an average particle diameter in the above range, the surface area can be increased and the contact area with the binder polymer can be increased. The average particle diameter of the catalyst particles can be measured visually with a transmission electron microscope.

  In the composite particles according to this embodiment, the catalyst particles are preferably supported by 1 to 99% by weight, more preferably 10 to 90% by weight, and still more preferably 20 to 80% by weight with respect to 100% by weight of the composite particles. Preferably it is. By adjusting the supported amount of catalyst particles within the above range, the desired catalytic activity tends to be easily obtained.

  The composite particles according to this embodiment may be produced by a conventional method in which catalyst particles are supported on solid particles, or commercially available products may be obtained. Examples of commercially available composite particles include Tanaka Kikinzoku Kogyo Co., Ltd., trade name “TEC10E40E”, Degussa Co., Ltd., trade name “F101RA / W”.

The content of the composite particle in the electrode catalyst layer, the area of the one main surface of the electrode catalyst layer is preferably 0.001 to 10 mg / cm ^2, more preferably 0.01 to 5 mg / cm ² More preferably, it is 0.1-1 mg / cm < ² >. Since the power generation amount depends on the total area of the catalyst particles, that is, the mass, it is easy to obtain high power generation characteristics by setting the composite particle content to 0.001 mg / cm ² or more. Moreover, since the voltage loss due to the proton conduction resistance of the electrolyte can be suppressed by setting the content of the composite particles to 10 mg / cm ² or less, higher power generation characteristics tend to be obtained.

  The mass ratio of the polymer electrolyte to the catalyst particles is preferably 0.1 or more, more preferably 0.5 or more, from the viewpoint of improving proton conductivity. The mass ratio is preferably 10 or less, more preferably 2 or less, from the viewpoint of improving the electron conductivity and the fuel gas diffusibility.

  The thickness of the electrode catalyst layer of the present embodiment is preferably 0.1 to 50 μm, more preferably 0.5 to 30 μm, and still more preferably 1 to 20 μm. When the thickness is 0.1 μm or more, it becomes easy to form an electrode catalyst layer having a catalyst carrying amount capable of exhibiting sufficient power generation performance. In addition, when the thickness is 50 μm or less, it is possible to suppress a decrease in gas diffusibility in the electrode catalyst layer and to reduce electric resistance. In addition, the thickness of an electrode catalyst layer can be measured with a contact-type film thickness meter.

  The electrode catalyst layer of the present embodiment has a porosity of preferably 1% by volume or more, more preferably 10% by volume or more, and still more preferably 20% by volume or more, from the viewpoint of improving ion conductivity. . Further, from the viewpoint of improving the diffusibility of water generated by fuel gas and power generation, the porosity is preferably 99% by volume or less, more preferably 90% by volume or less, and further preferably 80% by volume or less. preferable. The porosity of the electrode catalyst layer can be measured by a mercury intrusion method.

Next, the manufacturing method of the membrane electrode assembly which concerns on this embodiment is demonstrated. It does not specifically limit as a manufacturing method of a membrane electrode assembly, A conventionally well-known manufacturing method may be sufficient. For example, when the polymer electrolyte contained in the electrode catalyst layer is a perfluorocarbon sulfonic acid resin, it is desirable to obtain a membrane electrode assembly by a method including the following steps (1) to (3). That is, (1) a step of obtaining a perfluorocarbon sulfonic acid resin solution by dissolving or suspending the perfluorocarbon sulfonic acid resin in a solvent, and (2) mixing in which the perfluorocarbon sulfonic acid resin solution, the above composite particles and the solvent are mixed. Preferably, the method includes a step of obtaining a liquid, and (3) a step of forming an electrode catalyst layer on the polymer electrolyte membrane using the mixed solution to obtain a membrane electrode assembly.
Hereinafter, each step will be described.

(Process 1)
In step 1, a perfluorocarbon sulfonic acid resin is dissolved or suspended in a solvent to obtain a perfluorocarbon sulfonic acid resin solution that is a polymer electrolyte solution. The perfluorocarbon sulfonic acid resin solution includes a perfluorocarbon sulfonic acid resin suspension obtained by suspending a perfluorocarbon sulfonic acid resin in a solvent. More specifically, the state of the perfluorocarbon sulfonic acid resin solution is an emulsion in which liquid particles are dispersed as colloidal particles or coarser particles in the liquid to form a milky state, and solid particles are colloidal particles in the liquid. Or a suspension dispersed as particles that can be seen under a microscope, a colloidal liquid in which macromolecules are dispersed, or a micellar liquid that is a lyophilic colloidal dispersion system formed by associating many small molecules with intermolecular forces Are also included. The perfluorocarbon sulfonic acid resin solution may be in one of these states or in a combination of two or more.

  As the solvent, a solvent having good affinity with the perfluorocarbon sulfonic acid resin is preferable, and specifically, a protic organic solvent represented by water, ethanol, methanol, n-propanol, isopropyl alcohol, butanol, and glycerin; Examples include aprotic solvents such as N, N-dimethylformamide, N, N-dimethylacetamide, and N-methylpyrrolidone. These are used singly or in combination of two or more. When one type of solvent is used, water is particularly preferable as the solvent. Moreover, when using in combination of 2 or more types of solvent, the liquid mixture of water and a protic organic solvent is especially preferable.

  The method for dissolving or suspending the perfluorocarbon sulfonic acid resin in the solvent is not particularly limited. For example, first, a perfluorocarbon sulfonic acid resin is added to a solvent (for example, a mixed solvent of water and a protic organic solvent) to obtain a composition. Next, the obtained composition is housed in an autoclave having a glass inner cylinder as necessary, and after replacing the air inside the autoclave with an inert gas such as nitrogen, the internal temperature is 50 ° C to 250 ° C. Heat and stir under conditions 0.25-12 hours. Thereby, a perfluorocarbon sulfonic acid resin solution is obtained. The total solid content concentration in the perfluorocarbon sulfonic acid resin solution is preferably 0.5 to 50% by mass, more preferably 1 to 50% by mass, further preferably 3 to 40% by mass, and 5 to 30% by mass. % Is particularly preferred. When the total solid content concentration is 0.5% by mass or more, the yield of the electrode catalyst layer tends to be improved. When the total solid content concentration is 50% by mass or less, handling difficulty associated with increase in viscosity and undissolved matter. It tends to be possible to suppress the occurrence of.

  When using a mixture of water and a protic organic solvent as the solvent, the mixing ratio depends on the dissolution method, dissolution conditions, type of perfluorocarbon sulfonic acid resin, total solid content concentration, dissolution temperature, stirring speed, etc. It is selected appropriately. However, when the amount of the protic organic solvent is increased, the solution viscosity is increased, and when the amount of water is increased, it is difficult to dissolve. Therefore, the mass ratio of the protic organic solvent to water is preferably 0.1 to 10, and 0.1 It is more preferable that it is ~ 5.

  The perfluorocarbon sulfonic acid resin solution may be concentrated before being subjected to step 2. Although it does not specifically limit as a method of concentration, For example, the method of heating the perfluorocarbonsulfonic acid resin solution to volatilize a solvent, and the method of concentrate | evaporating under reduced pressure are mentioned. The total solid concentration in the perfluorocarbon sulfonic acid resin solution obtained by concentration is preferably 0.5 to 50% by mass, more preferably 1 to 50% by mass, and further preferably 3 to 40% by mass. 5 to 30% by mass is particularly preferable. If the total solid content concentration is 0.5% by mass or more, the yield of the electrode catalyst layer tends to be improved. If the total solid content concentration is 50% by mass or less, it is difficult to handle due to increase in viscosity and undissolved matter. It tends to be able to suppress the occurrence.

  The non-concentrated or concentrated perfluorocarbon sulfonic acid resin solution obtained as described above may be further filtered. By filtering, it is possible to remove undissolved polymer, gelled polymer, large dispersed polymer, or dust mixed during the process until a perfluorocarbon sulfonic acid resin solution is obtained. It does not specifically limit as a filter medium used for filtration, For example, a polypropylene, polyester, polytetrafluoroethylene, and a cellulose are mentioned. The pore diameter of the filter medium is not particularly limited, and may be in the range of 0.5 to 100 μm, for example.

(Process 2)
In step 2, a mixed liquid obtained by mixing the perfluorocarbon sulfonic acid resin solution, the above-described composite particles, and a solvent, that is, an electrode catalyst composition for a fuel cell (hereinafter also referred to as “electrode catalyst composition”) is obtained. They are mixed by a conventional method, and in order to improve the dispersibility of the perfluorocarbon sulfonic acid resin solution and the composite particles in a solvent, they may be dispersed using various apparatuses. Examples of the apparatus include a homogenizer, a ball mill, ultrasonic treatment, and pressure dispersion treatment.

Examples of the solvent for the electrode catalyst composition include water, lower alcohols such as ethanol, 1-propanol, and 2-propanol, ethylene glycol, propylene glycol, glycerin, and dimethyl sulfoxide, and preferably water, ethanol, and 1-propanol. These are used singly or in combination of two or more. The electrode catalyst composition preferably has a lower alcohol solvent amount (lower alcohol / SO ₃ H) (molar ratio) per mole of sulfonic acid unit of the perfluorocarbon sulfonic acid resin of 100 or more, more preferably 170 or more. When the ratio is 100 or more, gelation of the composition tends to be suppressed. This gelling suppression effect is remarkable in an electrode catalyst composition containing a perfluorocarbon sulfonic acid resin having an equivalent weight of 250 to 680. On the other hand, in an electrode catalyst composition containing a perfluorocarbon sulfonic acid resin having an equivalent weight of 700 or more, gelation does not proceed remarkably even when the ratio is less than 100, and a highly fluid product is obtained.

(Process 3)
In step 3, an electrode catalyst layer is formed on the polymer electrolyte membrane using the above mixed solution to obtain a membrane electrode assembly. The membrane electrode assembly of the present embodiment is formed by applying an electrode catalyst composition, which is a mixed solution containing a perfluorocarbon sulfonic acid resin solution and composite particles, onto a polymer electrolyte membrane to form an electrode catalyst layer. It can be obtained by drying and heat treatment. Alternatively, the electrode catalyst composition is coated on a substrate, for example, a polytetrafluoroethylene (PTFE) sheet, and further subjected to drying and heat treatment to obtain an electrode catalyst layer. By laminating and bonding to the membrane, the membrane electrode assembly of this embodiment is obtained. In this case, the electrode catalyst layer and the polymer electrolyte membrane can be bonded by heating and pressing at 100 to 200 ° C. in the stacking direction.

  As a method for applying the electrode catalyst composition, for example, various generally known application methods such as a spray method and a screen printing method can be used.

  From the viewpoint of improving the hot water solubility of the electrode catalyst layer of the present embodiment obtained as described above, it is preferable to heat-treat the electrode catalyst layer after forming the electrode catalyst layer in step 3. The heating temperature of the electrode catalyst layer in this heat treatment is preferably 130 to 200 ° C, more preferably 150 to 180 ° C. The heating temperature is preferably 130 ° C. or higher from the viewpoint of suppressing dissolution of the electrode catalyst layer in hot water and battery performance, and 200 ° C. or lower from the viewpoint of suppressing thermal oxidative decomposition of the polymer electrolyte.

  Moreover, the heating time of the electrode catalyst layer in this heat treatment is preferably 3 to 120 minutes, and more preferably 5 to 90 minutes. The heating time is preferably 5 minutes or longer from the viewpoint of suppressing dissolution of the electrode catalyst layer in hot water and battery performance, and 120 minutes or shorter from the viewpoint of suppressing thermal oxidative decomposition of the polymer electrolyte.

  The type of the polymer electrolyte membrane provided in the membrane electrode assembly of the present embodiment is not particularly limited, but a polymer electrolyte having the same molecular structure as the polymer electrolyte constituting the electrode catalyst layer provided in the membrane electrode assembly is used. The polymer electrolyte membrane contained is preferred.

Further, such a polymer electrolyte membrane contains 0.1 to 10% by mass of a polymer having a polyazole and / or a thioether group, or instead of / in addition to the known active radical scavenger or H ₂ O ₂ decomposition. It is preferable to contain a substance having a catalytic action from the viewpoint of chemical stability. Moreover, the film | membrane reinforced with the well-known reinforcing material may be sufficient. It should be noted that, even in the case of an electrolyte membrane containing a known hydrocarbon electrolyte, according to the present embodiment, if necessary, a bonding layer or the like that does not affect ion conduction is provided for the bonding. It can be used as a polymer electrolyte membrane.

  Furthermore, although there is no restriction | limiting in particular as EW of such a polymer electrolyte membrane, It is preferable that it is 250-1200, and it is more preferable that it is 250-900. Moreover, as a film thickness, it is preferable in it being 1-500 micrometers, it is more preferable in it being 2-100 micrometers, and it is still more preferable in it being 5-50 micrometers.

  The membrane electrode assembly according to the present embodiment may further include a pair of gas diffusion layers outside each electrode catalyst layer as necessary. When the membrane / electrode assembly includes a gas diffusion layer, the gas diffusion layer may be bonded by heating and pressing the electrode catalyst layer in the same manner as the electrode catalyst layer and the polymer electrolyte membrane are bonded.

  The solid polymer electrolyte fuel cell according to the present embodiment includes components used for a general solid polymer fuel cell such as a bipolar plate and a backing plate, except that the membrane electrode assembly according to the present embodiment is provided. Can be provided.

  Of these, the bipolar plate is graphite or a composite material of graphite and resin, a metal plate, or the like in which grooves for allowing a gas such as fuel or oxidant to flow are formed on the surface thereof. In addition to the function of transmitting electrons to an external load circuit, the bipolar plate has a function as a flow path for supplying fuel and an oxidant to the vicinity of the electrode catalyst.

  For example, the solid polymer electrolyte fuel cell according to the present embodiment is manufactured by stacking a plurality of composites each including a pair of bipolar plates and an MEA inserted between the bipolar plates.

  The solid polymer electrolyte fuel cell is operated by supplying hydrogen to one electrode and oxygen or air to the other electrode.

  The solid polymer electrolyte fuel cell according to the present embodiment has good output characteristics even under an operating temperature of 80 to 90 ° C., an anode humidification temperature of 60 ° C., and no cathode humidification conditions, for example. The detailed reason is not clear, but by making the water content of the cathode polymer electrolyte larger than the water content of the anode polymer electrolyte, the water generated in the fuel cell operation passes through the polymer electrolyte membrane, It is thought to promote the reverse diffusion of water moving from the cathode side to the anode side. As a result, the proton conductivity of the polymer electrolyte membrane is increased, and it is considered that high output characteristics can be obtained under the non-humidified condition of the cathode.

  The electrode catalyst layer of the present embodiment is provided for chloralkali, water electrolysis, hydrohalic acid electrolysis, salt electrolysis, oxygen concentrator, humidity sensor, gas sensor, etc. in addition to the use as a fuel cell electrode catalyst layer. It can also be used as an electrode catalyst layer.

  As mentioned above, although the form for implementing this invention was demonstrated, this invention is not limited to the said form, It can implement in various deformation | transformation within the range of the summary.

  Hereinafter, although this Embodiment is demonstrated concretely based on an Example, this Embodiment is not restrict | limited to the following Example.

(Measurement of water content in water at 25 ° C)
The polymer electrolyte was left in water at 25 ° C. for 1 hour, then taken out from the water, wiped off water droplets on the surface, and weighed (water content). Subsequently, the polymer electrolyte was dried at 160 ° C., and the mass after drying was weighed (dry mass). The mass increase rate of the moisture content with respect to the dry mass was calculated and used as the moisture content in water at 25 ° C. It shows that water content is so high that the numerical value of 25 degreeC water content is high.

(Measurement of EW)
The polymer electrolyte was immersed in 30 mL of a saturated aqueous NaCl solution at 25 ° C. and left for 30 minutes with stirring. Subsequently, the proton in the saturated NaCl aqueous solution was neutralized and titrated using 0.01N aqueous sodium hydroxide solution using phenolphthalein as an indicator. The electrolyte membrane obtained after neutralization titration in which the counter ion of the sulfonic acid group was in the form of sodium ion was rinsed with pure water, further vacuum-dried, and weighed. The amount of sodium hydroxide required for neutralization is M (mmol), and the weight of the electrolyte membrane in which the counter ion of the sulfonic acid group is sodium ion is W (mg). The weight EW (g / eq) was determined.
EW = (W / M) −22 (A)

(Measurement of proton conductivity)
The proton conductivity of the polymer electrolyte was measured using a polymer membrane moisture test apparatus MSB-AD-V-FC (trade name) manufactured by Nippon Bell Co., Ltd.

(Measurement of melt flow rate (MFR))
The MFR of the precursor of the polyelectrolyte was measured using MELT INDEXER TYPE C-5059D (trade name, manufactured by Toyo Seiki Co., Ltd.) under the conditions of 270 ° C. and a load of 2.16 kg according to ASTM standard D1238. As a unit of MFR, the mass of the extruded precursor was expressed in grams per 10 minutes.

(Fuel cell evaluation)
In order to investigate the cell characteristics of the membrane electrode assembly, the following fuel cell evaluation was performed. First, the anode-side gas diffusion layer and the cathode-side gas diffusion layer were made to face each other, and the membrane electrode assembly was sandwiched between them, and incorporated in the evaluation cell. Carbon paper (GDL35BC, manufactured by SGL Carbon Co.) was used as the gas diffusion layer on the anode side and the cathode side. This evaluation cell was installed in an evaluation apparatus (Toyo Technica Co., Ltd.) and evaluated under the following conditions 1 and 2.
(Condition 1) Cell temperature 80 ° C., anode humidification temperature 60 ° C., cathode non-humidification (Condition 2) Cell temperature 90 ° C., anode humidification temperature 60 ° C., cathode non-humidification Supplied. The air gas was supplied directly from the air gas cylinder to the evaluation cell. Under each condition, the evaluation cell was held at a voltage of 0.25 A / cm ² for 30 minutes, and then the voltage and resistance were measured. At this time, the gas flow rate was set so that the utilization rate of hydrogen gas was 75% and the utilization rate of air gas was 55%.

Example 1
(Preparation of perfluorocarbon sulfonic acid resin precursor)
A stainless steel stirring autoclave was charged with a 10% aqueous solution of C ₇ F ₁₅ COONH ₄ and pure water, and after sufficient vacuum and nitrogen substitution, tetrafluoroethylene (CF ₂ = CF ₂ ) (hereinafter referred to as “TFE”). The gas was introduced and the pressure was increased to 0.7 MPa with a gauge pressure. Subsequently, polymerization was initiated by injecting an aqueous ammonium persulfate solution. In order to replenish the TFE consumed by the polymerization, the TFE gas is continuously supplied to maintain the pressure of the autoclave at 0.7 MPa, and the mass ratio is 2.00 times the supplied TFE. A corresponding amount of CF ₂ ═CFO (CF ₂ ) ₂ —SO ₂ F was continuously supplied for polymerization. Thus, pellets of a perfluorocarbon sulfonic acid resin precursor were obtained. Also, except for changing the mass ratio of the supplied _{CF 2 = CFO (CF 2)} 2 -SO 2 F from 2.00 to 0.70 in the same manner as described above, pellets of different perfluorocarbon sulfonic acid resin precursor Got.

(Preparation of perfluorocarbon sulfonic acid resin solution)
Perfluorocarbon sulfonic acid resin precursor pellets obtained as described above were prepared. These pellets were contacted at 80 ° C. for 20 hours in an aqueous solution in which potassium hydroxide (15% by mass) and methyl alcohol (50% by mass) were dissolved to perform a hydrolysis treatment. Then, those pellets were taken out from the aqueous solution, immersed in 60 ° C. water for 5 hours, and taken out from the water. Next, the treatment of immersing these pellets in a 2N aqueous hydrochloric acid solution at 60 ° C. for 1 hour was repeated 5 times by updating the aqueous hydrochloric acid solution every time, and then washed with ion-exchanged water and dried. Accordingly, the repeating unit represented by — (CF ₂ —CF ₂ ) — having EW different from each other and represented by — (CF ₂ —CF (—O— (CF ₂ ) ₂ —SO ₃ H)) — The pellets of perfluorocarbon sulfonic acid resins A1 and A2 having the above repeating units were obtained.

  The EW of the perfluorocarbon sulfonic acid resin after hydrolysis and acid treatment was 455 for A1 and 720 for A2. The MFR (measured with the precursor) of these resins was 0.4 for A1 and 3.0 for A2. The water content of these resins in water at 25 ° C. was 337 mass% for A1 and 36 mass% for A2. The proton conductivity of these resins at 120 ° C. and 30% RH was 0.09 S / cm for A1 and 0.02 S / cm for A2.

  Perfluorocarbon sulfonic acid resin pellets were placed in a 5 L autoclave together with an aqueous ethanol solution (water: ethanol = 50: 50 (mass ratio)), sealed, heated to 160 ° C. with stirring with a blade, and held for 5 hours. Thereafter, the autoclave was naturally cooled to prepare a 5% by mass uniform perfluorocarbon sulfonic acid resin dispersion. Next, 100 g of pure water was added to 100 g of perfluorocarbon sulfonic acid resin dispersion and stirred, and then this liquid was heated to 80 ° C. and concentrated while stirring until the solid content concentration became 20% by mass. A 20% perfluorocarbon sulfonic acid resin dispersion was obtained. The dispersion of resin A1 is AS1, and the dispersion of resin A2 is AS2.

(Production of membrane electrode assembly)
For 1.00 g of Pt-supported carbon (trade name “TEC10E40E”, trade name “TEC10E40E”, supported by Tanaka Kikinzoku Co., Ltd.), 2.0 g of 20% perfluorocarbon sulfonic acid resin solution AS1 or AS2, and 8.4 g of ethanol. After the addition, electrode ink was obtained by mixing well with a homogenizer. The electrode ink obtained from the resin solution AS1 is BS1, and the electrode ink obtained from the resin solution AS2 is BS2.
The electrode ink BS1 was applied to one surface of a polymer electrolyte membrane (trade name “ion exchange membrane-SF7203”, 20 μm, manufactured by Asahi Kasei E-Materials Co., Ltd.) by screen printing, and this was used as a cathode catalyst layer. Electrode ink BS2 was applied to the other surface of the polymer electrolyte membrane by a screen printing method to form an anode catalyst layer. The coating amount was such that both the Pt loading amount and the polymer loading amount were 0.3 mg / cm ² in the cathode catalyst layer, and both the Pt loading amount and the polymer loading amount were 0.2 mg / cm ^{2 in} the anode catalyst layer. It adjusted so that it might become. After coating, a membrane electrode assembly including a polymer electrolyte membrane, an anode catalyst layer and a cathode catalyst layer sandwiching the polymer electrolyte membrane was obtained by performing a heat treatment at 140 ° C. for 5 minutes at room temperature for 1 hour.

Using this membrane electrode assembly, fuel cell evaluation was performed as described above. The results are shown in Table 1. The voltage was 0.745 V under condition 1 and 0.659 V under condition 2, indicating a high voltage even in the cathode non-humidified condition. Resistance at that time, 157mΩ · cm ² under the conditions 1 was 343mΩ · cm ² under the conditions 2.

(Comparative Example 1)
A membrane electrode assembly was prepared in the same manner as in Example 1 except that BS2 was used for both of the electrode inks for forming the cathode catalyst layer and the anode catalyst layer, and the fuel cell was evaluated. As a result, the voltage was 0.701 V under condition 1 and 0.540 V under condition 2, and the voltage was lower than that in Example 1 under the non-humidifying condition of the cathode. Resistance at that time, 198mΩ · cm ² under the conditions 1, the condition 2 is 544mΩ · cm ^2, the resistance is increased as compared with Example 1.

(Comparative Example 2)
A membrane / electrode assembly was prepared in the same manner as in Example 1 except that BS1 was used as the electrode ink for forming the cathode catalyst layer and the anode catalyst layer, and the fuel cell was evaluated. As a result, the voltage was 0.708 V under condition 1 and 0.558 under condition 2, and the voltage was lower than that of Example 1 under the non-humidifying condition of the cathode. Resistance at that time, 201mΩ · cm ² under the conditions 1, the condition 2 is 548mΩ · cm ^2, the resistance is increased as compared with Example 1.

(Comparative Example 3)
A membrane electrode assembly was prepared in the same manner as in Example 1 except that BS2 was used for the electrode ink of the cathode catalyst layer and BS1 was used for the electrode ink of the anode catalyst layer, and the fuel cell was evaluated. As a result, the voltage was 0.684 V under condition 1 and 0.321 under condition 2, and the voltage was lower than in Example 1 under the non-humidifying condition of the cathode. Resistance at that time, 206mΩ · cm ² under the conditions 1, the condition 2 is 1050mΩ · cm ^2, the resistance is increased as compared with Example 1.

  As is clear from the results of Example 1 and Comparative Examples 1 to 3, the water content of the polymer electrolyte in the cathode catalyst layer at 25 ° C. is larger than the water content of the polymer electrolyte in the anode catalyst layer at 25 ° C. in water. As a result, it was confirmed that a high output can be obtained under the non-humidified condition of the cathode.

  The membrane / electrode assembly of the present invention has a high output under conditions of no cathode humidification, for example, under conditions of an operating temperature of 80 to 90 ° C., an anode humidification of 60 ° C., and no cathode humidification. Therefore, by providing the membrane electrode assembly of the present invention, it is possible to provide a solid polymer electrolyte fuel cell or the like in which a humidifier is omitted.

Claims (2)

Sandwiching a polymer electrolyte membrane, the polymer electrolyte membrane from both sides, the anode catalyst layer, a cathode catalyst layer, comprising a membrane electrode assembly comprising a solid polymer electrolyte type of operating a cathode electrode without humidification under conditions A fuel cell,
In the membrane electrode assembly,
The anode catalyst layer and the cathode catalyst layer each include composite particles including conductive particles and electrode catalyst particles supported thereon, and a polymer electrolyte,
The composite particles carry 1 to 99% by mass of the electrode catalyst particles with respect to 100% by mass of the composite particles,
The water content of the polymer electrolyte in the anode catalyst layer at 25 ° C. in water is 20 to 36%,
The water content in water at 25 ° C. of the polymer electrolyte in the cathode catalyst layer is 2 to 20 times greater than the water content in water at 25 ° C. of the polymer electrolyte in the anode catalyst layer,
The equivalent weight of the polymer electrolyte in the cathode catalyst layer, Ri 455-800 der,
The polymer electrolyte in the cathode catalyst layer is a perfluorocarbon sulfonic acid resin, and the perfluorocarbon sulfonic acid resin has the following general formula (1):
_{- (CF 2 -CFZ) - (} 1)
(In formula, Z shows a hydrogen atom, a chlorine atom, a fluorine atom, or a C1-C3 perfluoroalkyl group.)
A repeating unit represented by the following general formula (2):
_{- (CF 2 -CF (-O- (} CF 2) m -SO 3 H)) - (2)
(In the formula, m is an integer of 1 to 12.)
A copolymer having a repeating unit represented by:
Solid polymer electrolyte fuel cell . 2. The solid polymer electrolyte fuel cell according to claim 1, wherein an equivalent weight of the polymer electrolyte in the cathode catalyst layer is 100 to 1000 smaller than an equivalent weight of the polymer electrolyte in the anode catalyst layer.